Monolithic microwave integrated circuit (MMIC) packaging and interconnects have a significant effect on the electrical performance of high frequency systems such as microwave systems and thus it is important to characterize microwave transitions independently of the embedded circuits.
In general, three different techniques have been developed for performing such characterizations of MMIC packaging and interconnects. The first technique determines bolometer mount efficiency by using radio frequency (RF) measurements of a barretter at different bias states to calculate the efficiency (Power.sub.out /Power.sub.in) of the mount. This is accomplished by varying the DC voltage on the bolometer mount and then computing the efficiency from the barretter resistance and the reflection coefficient for each DC operating point. One disadvantage is that the technique does not provide any information with respect to the scattering parameters (S-parameters) of the transition, and such S-parameter information is more useful to an engineer than the efficiency of the device. This technique is discussed in G. F. Engen, A Bolometer Mount Efficiency Measurement Technique, Journal of Research of the National Bureau of Standards, vol. 65C, no. 2, April-June 1961.
The second, and most popular, technique is to solder or epoxy into the MMIC package a test fixture which utilizes a single transmission line as a standard. By using only one line, the amount of information that can be obtained is limited and not enough information is provided to fully characterize the package transitions. To augment the information provided, a mathematical model must be created for the package in order to determine the S-parameters. Further, the use of a straight transmission line imposes two physical restrictions on the device being tested. First, the distance between the transitions must remain fixed for all devices being characterized. Second, the orientation of the transitions must be symmetrical about the axis of the line. These two restrictions impose the requirements that the number of transitions in a package must be even and a transition must be located opposite another transition at a fixed distance. This technique is discussed in P. B. Ross and B. D. Geller, A Broadband Microwave Test Fixture, Microwave Journal, Vol. 30, No. 5, May 1987, pp. 233-248.
The third technique uses a least-squares de-embedding algorithm to characterize microwave transitions from measured S-parameters. The characterization procedure outlined in the literature uses multiple insertions into the package. In many cases, however, the standards need to be soldered or epoxied into the package or interconnect. This makes insertion difficult and the use of multiple standards impractical. Multiple insertions also degrade the accuracy of the package or interconnect characterization. This technique is discussed in R. F. Bauer and P. Penfield, De-embedding and Unterminating, IEEE Transactions on Microwave Theory and Techniques, vol. MTT-22, no. 3, pp. 282-288, March 1974.
Several U.S. patents disclose test fixtures which use the second technique discussed above in the characterization of high frequency circuits. For example, U.S. Pat. No. 4,947,111 (Higman et al.) discloses a test fixture comprising a conductive alignment plate having a plurality of apertures therein which match the signal conductor pins of the MMIC package. Signal conductor pins pass through the apertures and form sections of a transmission line. The apertures are sized such that the impedance of these sections of the transmission line effectively matches the 50 ohm resistance of the internal interconnect to the MMICs within the package.
U.S. Pat. No. 4,980,636 (Romanofsky et al.) discloses a MMIC test fixture having a support structure which is spring biased for testing MMIC chips. A set of calibration standards are provided.
U.S. Pat. No. 4,897,601 (Hirsch et al.) discloses an apparatus for providing an RF contact between the ground plane surface of a MMIC chip and a test fixture. The apparatus utilizes a single transmission line to provide calibration standards for the MMIC chips.
U.S. Pat. No. 5,051,810 (Katoh) discloses a semiconductor device for performing frequency characteristic tests. The semiconductor has a substrate that includes input, output and grounding electrode pads which provide contact points for a probe needle of a conventional high frequency wafer probe.
U.S. Pat. No. 4,704,872 (Jones) discloses a thermally controlled transmit/receive (T/R) module test apparatus which enables acquiring MMIC T/R module data, such as S-parameters and noise figure as a function of thermal cycling.